The present invention relates to electric meters; and more particularly, it relates to an electric meter capable of recording the consumption of electric energy on one or more registers which are engaged only at certain times during the day. Such meters may be used, for example, to bill consumption of energy during peak use hours at a different rate than energy which is consumed during non-peak or "off" periods when demand is reduced. It is known that there are certain times during the day and certain periods during the week when electrical energy is in greater demand, and utilities must provide generating capacity in accordance with the maximum anticipated demand. By having different billing rates for different periods depending upon demand, the utility company can encourage the switching of loads to non-peak periods as well as apportion the cost of increased capital equipment to the customers whose demand has forced the increased capacity.
Multiple rate metering of electrical energy usage has been suggested as a means of setting proper billing rates. Some attempts have been specifically directed to applying dual rates with the higher rate being determined by a clock so that the rates are applied as a function of the time of day. Other attempts have been to measure the maximum usage by a particular customer during a predetermined interval (called "demand"), and then to apply a rate as a function of the maximum demand reading during a given billing period.
One system uses a programmed control circuit having a seven-day clock for performing the timing functions to engage and disengage drive gears for alternate rate decade-dial registers. This is disclosed in U.S. Pat. No. 4,050,020, granted Sept. 20, 1977.
The present invention is designed for use with a meter which includes a kilowatthour register which is continuously engaged as well as at least one special register which is selectively engageable. The special register may either be a kilowatthour (energy) or demand register. Further, two such registers may be used so that the combination of a selectively engageable energy meter and a selectively engageable demand meter may be used, or two selectively engageable energy meters may be used, one to record, for example, during periods of moderate demand, and the other to be used only during periods of peak demand.
A programmable memory (which may be Read Only Memory or ROM) stores calendar data representative of schedule events and the times (called "calendar" times, as distinguished from real time) at which such events are to be effected or implemented. A schedule event may be the engagement of a special register, or the controlling of a load under customer programming, or simply the illumination of an indicator light to let the customer know that a special rate is being applied or activating the display.
A data processor including a Central Processor Unit (CPU) derives timing information from the line frequency and generates real time data in a first file. The CPU compares real time data with calendar time from the ROM on a continuous basis. When real time equals calendar time, the CPU implements the event by energizing an appropriate register selection circuit or display circuit, or energizing an appropriate output lead, and addresses the next schedule event in the calendar memory. Preferably, the calendar times are stored in the calendar memory in chronological order so that the next calendar time is retrieved simply by incrementing an address register. This arrangement further facilitates the CPU's re-initializing (that is, synchronizing) the calendar ROM with real time, as will be described.
The system includes a visual display, preferably employing Light Emitting Diodes (LEDs), for displaying real time data when actuated by the operator. For this purpose, a Display Selection Switch and a Display Set Switch are also provided, accessible from the front of the meter. When the selection switch (referred to as S1) is actuated, the system enters a command display mode in which three separate time words are displayed, all representative of real time at which the system is set. Word I includes the minute and hour. Word II includes the day of the month and month. Word III includes the day of the week and the year (in two digits). Each time the Display Selection Switch is actuated, the CPU advances to the next word portion. If the Display Set Switch (S2) is depressed first, the system enters a mode of operation in which the real time data can be set. In this mode, switch S2 is used to select the data to be set from Words I, II or III and flashes that selected portion on the display. Switch S1 is then used to set that data by incrementing it.
As mentioned, the CPU derives timing data from an external timing source which, in turn, derives timing signals from the line source. A timing circuit receives the line frequency signal; and, by means of a count down circuit or counter, it counts the line frequency and generates an output pulse at a repetition rate of one per second. This timing signal as well as the output of the display switches mentioned above are coupled to the CPU through a multiplexer unit which is selected or addressed by the CPU itself. In addition to the use of a counter circuit to reduce the effect of line noise on internal timing functions, the program for the CPU takes approximately one second to complete. Program delays comprise 0.5 seconds, and this comprises a refractory time during which the CPU will not respond to timing interrupts. Hence, the effects of external noise signal on the timing of the CPU are reduced.
In the event of a power outage, the system switches over to a battery, and derives timing from the crystal clock for the CPU. Further, during battery carry over the visual display is disabled, and the system does not energize any of the special registers or the external signal lead.
The CPU stores real time data in a file in random access memory, and it also stores the time of the next event to be implemented, to be referred to as "calendar time". The program is designed such that if real time exceeds calendar time, the CPU will continue to increment the address in the calendar memory until calendar time exceeds real time. At a certain time every day (at midnight, for example) the CPU resets the contents of the calendar time file to zero. The program detects that real time is greater than calendar time and sequences through the calendar Read Only Memory (ROM) until it retrieves the next calendar event. Thus, the system re-initializes itself at least once a day.
Further, if the Display Set Switch is actuated even once, the CPU resets the contents of the calendar time file to zero so that re-initialization is automatically implemented. This also occurs if the calendar ROM is removed. That is to say, the calendar ROM has an output with a specific signal on it which is identified by the CPU. If that signal is not present the CPU senses this and resets the contents of the calendar time file to zero so that when a calendar ROM is then placed in the meter, re-initialization is automatic. This has the further advantage that a separate ROM, called an AUTOSET ROM may have a separate identification number other than "0" (for no ROM), or "1" (for calendar ROM), to identify the AUTOSET ROM. The AUTOSET ROM is used to automatically load real time into the CPU, and it does so by first clearing the real time and transferring the contents of the calendar time file into the real time file. This is done cyclically so that both the calendar time file and the real time file contain real time. When the AUTOSET ROM is removed, transients will not interfere because the last transfer of information will have been into the calendar time file, not the real file time file which will have been undisturbed. When a calendar ROM is then inserted, re-initialization is implemented so whatever was stored in the calendar time file will have been discarded anyway.
In a preferred embodiment, the calendar ROM contains data for up to six separate schedules permitting eight changes daily. The schedules in the exemplary embodiment include one schedule for weekdays, one for Saturdays, and one for Sundays/holidays. Further, a winter and a summer seasonal change are permitted. Events can be programmed on the quarter hour, and provision is also made for the beginning and end of daylight saving time. Demand intervals can be set to 15, 30 or 60 minutes, and the demand reset period can be set accordingly. A full four year calendar is provided in each calendar ROM.
Other features and advantages will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.